In view of the increasing importance of polymers as substitutes for conventional materials of construction such as glass, metal, paper, and wood, the perceived need to convert non-renewable resources such as petroleum and dwindling amount of landfill capacity available for the disposal of waste products, considerable attention has been devoted in recent years to the problem of recovering, reclaiming, recycling or in some way reusing mixed waste plastics.
It has been proposed to pyrolyze or catalytically crack the mixed waste plastics so as to convert high molecular weight polymers into volatile compounds having much lower molecular weight. The volatile compounds, depending on the process employed, can be either relatively high boiling liquid hydrocarbons useful as fuel oils or fuel oil supplements or light to medium boiling hydrocarbons useful as gasoline-type fuels or as chemical “building blocks”.
U.S. Pat. No. 5,462,971 teaches a process for reclaiming a polyether polyol, comprising the steps of: (a) heating the polyether polyol and a zeolite-containing particulate catalyst in a fluidized bed reaction zone at a temperature effective to produce a volatile organic component and a spent catalyst component having carbon deposited thereon; (b) withdrawing a first stream comprising the volatile organic component from the reaction zone; (c) withdrawing a second stream comprising the spent catalyst component; and (d) heating the second stream in a regeneration zone in the presence of oxygen at a temperature effective to convert the carbon to carbon dioxide and water and to regenerate the catalyst.
It has also been proposed to pyrolyze or catalytically crack thermoset polymers so as to convert the high molecular weight polymers into volatile compounds having much lower molecular weight. U.S. Pat. No. 5,192,809 teaches a process for reclaiming a filled thermoset polymer, comprising the steps of: (a) heating particles of the polymer and a zeolite-containing particulate catalyst in a fluidized bed reaction zone at a temperature effective to produce a coarse filler component, coke, a volatile organic component, and a spent catalyst component; (b) withdrawing a first stream comprising the volatile organic component from the reaction zone; (c) withdrawing a second stream comprising the spent catalyst, the coke, and the coarse filler component from the reaction zone; (d) heating the second stream in a regeneration zone in the presence of oxygen at a temperature effective to convert the coke to carbon dioxide and water and to regenerate the catalyst; and (e) separating the regenerated catalyst and the coarse filler component.
It has been demonstrated that the pyrolysis of polyvinyl chloride (PVC) and polyvinylidene chloride (PVDC) can be performed in a two-step temperature program to minimize the formation of chlorinated hydrocarbons. The two-step temperature program eliminated the hydrogen chloride form the reactor and avoided the formation of chlorinated hydrocarbons in the liquid products. The two-step pyrolysis produced the plastic derived oils without halogenated hydrocarbons (less than 15 ppm). This work was published by Bhaskar, et al., in Green Chem., 2006, 8, 697-700.
U.S. Pat. No. 5,079,385 teaches a process for converting solid plastic materials into usable lower molecular weight hydrocarbonaceous materials by heating such plastic materials at elevated temperatures in effective contact with an acidic catalyst comprising at least one zeolite having acid activity. The catalyst may be comprised of ZSM-5 and at least one catalytic metal. The metal may be at least one of platinum, palladium, nickel, cobalt, iron, zinc, magnesium, molybdenum, tungsten, titanium, gallium, tantalum and chromium. The process claims co-feeding of hydrogen or a source of hydrogen to the reaction zone.